Induction foil cap sealers are well known. Referring to FIG. 1, a prior art induction foil cap sealer includes induction head 10 which includes a plurality of field coils 12. In operation, field coils 12 receive an electrical current which causes the development of magnetic fields that project away from field coils 12. The projected magnetic fields are schematically shown as circular lines surrounding field coils 12 for illustration purposes only. The magnetic fields projecting from field coils 12 are used for sealing a cap onto an opening of a bottle in the following manner.
Cap 14 is mechanically coupled to the opening of bottle 16 and placed under induction head 10. Due to the mechanical coupling between cap 14 and bottle 16, metallic foil 18, which is received in cap 14, is pressed between the end of cap 14 and the sealing edge of the opening of bottle 16. Included inside cap 14 is polymer sealing film 17 which is interposed between metallic foil 18 and the opening of bottle 16. Optionally, wax layer 20 and pulp board liner 22 are also included in cap 14 and sandwiched between metallic foil 18 and the closed end of cap 14.
To effect the seal, magnetic fields that project from field coils 12 permeate cap 14 and cause foil 18 to heat up. The heat so generated causes polymer sealing film 17 to melt and thus seal metallic foil 18 to the opening of bottle 16. As a result, a hermetic seal between metallic foil 18 and bottle 16 is obtained which can survive the removal of cap 14. If optional wax layer 20 is used, the generated heat melts wax layer 20 further enhancing the hermetic effect.
Induction head 10 may assume any number of shapes depending on the type of cap used. FIGS. 2A-2C illustrate three examples of induction heads.
Referring to FIG. 3, in a typical induction sealing operation, a series of bottles 16 are transported on a conveyor belt 24 under an induction head 10. Induction head 10 is included as part of induction sealer 27 and is positioned over conveyor belt 24. The number of bottles 16, the spacing of bottles 16, the space between cap 14 of a bottle 16 and induction head 10, and the speed of conveyor belt 24 can be selected to obtain the necessary heating for a proper seal for bottles 16 as they pass under induction head 10.
The sealing of each bottle 16 consumes an amount of power. As a plurality of bottles 16 pass under induction head 10 the power consumed is increased proportionally. Thus, as the number of bottles increases, and/or the spacing of bottles decreases, and/or the speed of the conveyor belt 24 increases more power is demanded by induction head 10. The amount of power demanded may also increase if the area of each metallic foil 18 is enlarged, i.e., when bottles 16 with larger openings are subjected to induction heating.
If the power demanded from induction head 10 exceeds the maximum power that induction head 10 is capable of providing, the quality of the hermetic sealing may be adversely affected due to insufficient power per bottle. Thus, quality control is sacrificed, which is commercially undesirable.
It is desirable to have a feature for monitoring the power consumption during sealing so that appropriate action can be taken in the event insufficient power is supplied to the bottles.